Brush mechanism



Oct. 28, 1952 w MlTCHELL 2,615,939

BRUSH MECHANISM Filed Oct. 2, 1950 WITNESSES: INVENTOR 504. William H. Mitchell.

7M. 47m BY 4 ATTORNEY Patented Oct. 2 8, 1952 BRUSH MECHANISM William H. Mitchell, Lima, Ohio, assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application October 2, 1950, Serial No. 187,909

4 Claims.

The present invention relates to brush mechanism for dynamoelectric machines, and more particularly to a low cost brush and spring construction for use in cartridge type brushholders.

Small universal motors of the fractional and sub-fractional horsepower sizes usually use brushholders of the cartridge type, consisting essentially of a tubular member in which the brush is axially movable, with a helical compression spring for applying an axial force to the brush to hold it in engagement with the commutator. In the conventional construction, the spring is attached to the brush by forcing the lower coils of the spring over a neck on the top of the brush, so that the spring and brush can be removed as a unit, thus facilitating replacement of the brushes. This is a simple, low cost construction, but it permits chattering of the brush on the commutator, which is often objectionable because of the noise, and because of the reduction in brush life caused by arcing.

Chattering of the brush can be prevented by providing a force normal to the axis of the brush, and acting in the direction of rotation of the commutator, to hold the brush against the side of the brushholder. Such a force can be provided by beveling the top of the brush, so that the top surface is inclined with respect to the brush axis, and the force exerted by the spring includes both an axial component and a component normal to the axis. When this has been done, however, it has not been possible to attach the spring to the brush, or to use the spring to conduct current to or from the brush, and it has been necessary to utilize a shunt molded or tamped in the top of the brush and soldered or otherwise secured to a special cap or button at the top of the brushholder, in order to make it possible to remove the brush and spring as a unit and to obtain good current conduction from the brush to the brushholder body. Such a brush construction, with a shunt and special cap, however, greatly increases the cost, the cost being about four times that of the simple spring construction first described. Such an increase in cost is extremely undesirable, and frequently cannot be tolerated, in these small motors which are built in large quantities at low cost and sold in a highly competitive market, so that even a relatively small increase in cost is a serious matter.

The principal object of the present invention is to provide a low cost brush mechanism, for use in cartridge type brushholders, which effectively prevents chattering of the brush.

Another object of the invention is to provide a low cost spring and brush construction, for use in cartridge type brushholders, in which chatter of the brush is prevented by providing an inclined or beveled top surface on the brush, but in which the shunt which has previously been necessary is eliminated, so that the cost is not increased.

Other objects and advantages of the invention will be apparent from the following detailed description, taken in connection with the accompanying drawing, in which:

Figure 1 is a vertical sectional View of a brushholder assembly embodying the invention, and

Fig. 2 is a transverse sectional view approximately on line IIII of Fig. 1.

The drawing shows a cartridge type brushholder having a tubular brushholder body I, which may be made of brass or other suitable conducting material. The brushholder body I is generally tubular, and has a rectangular axial slot 2, preferably formed by breaching to insure the desired accuracy. The slot 2 is made of the proper size to receive a brush 3, which is axially movable in the slot and which is adapted to engage a commutator indicated at 4. The brushholder body I is preferably supported in a sleeve or support member 5, which may be made of insulating material and which is adapted to be supported in the frame of a motor. The top o the support 5 is closed by acap 6 of insulating material which is threaded into the support 5, as shown, and which is provided with a slot 1 for a screwdriver to enable easy removal of the cap. The brushholder body I may, of course, be supported in other ways, as by mounting it on an insulating rocker ring in the motor, with the cap 6 threaded into a properly located opening in the motor frame.

As explained above, a force normal to the axis of the brush is necessary to prevent chattering of the brush 3 on the commutator 4, and such a force is provided by beveling the top of the brush 3, so that its upper surface 8 is inclined with respect to the axis of the brush, as clearly shown in Fig. 1. The brush is assembled in the brushholder with the high side of the brush pointing in the direction of rotation of the commutator 4, so that the brush will be held against the proper side of the brushholder body to positively prevent chattering. The required force is provided by a helical compression spring 9, which is made of a material, such as beryllium copper, having good electrical conductivity and the desired elastic properties. The upper end of the spring 9 has an enlarged coil I0, which is clamped between 3 the cap 6 and the top of the brushholder body i. The brush 3 has a hole i 1 extending transversely through it near the upper end, and the spring 9 is formed with a hook I2 at the lower end which is engaged in the hole H to loosely attach the spring to the brush.

It will be apparent that the spring 9 and brush 3 can be inserted in and removed from the brushholder as a unit, since the spring is attached to the brush by means of the hook l2, so that replacement of a brush is easily performed. The spring 9 is held in compression between the top surface 8 of the brush 3 and the cap 6, and because of the inclination of the top surface of the brush, the spring tends to curve and to slide or move to the low side of the brush until it comes in contact with the sideof the brushholder body I, as indicated in Fig. 1, this movement of the spring being permitted by its loose attachmerit to the brush by the hook H2. The spring thus urges the brush against the opposite side of the brushholder and exerts a force on the brush 3 which has an axial component, to hold the brush in engagement with the commutator, and a component normal to the brush axis, to hold the brush against the brushholder to prevent chattering of the brush. Since the spring 9 is held under pressure in direct contact with the top surface of the brush and with its upper end clamped against the top end of the brushholder body I, the spring itself provides good current conduction from the brush to the brushholder and no shunt or other additional current conducting means is required. The brushholder body I may have an annular groove it near its lower end for attachment of a lead by means of a garter spring or other suitable means.

It will be apparent that the brush and spring construction described provides a brush mechanism in which chatter of the brush is eliminated, but the cost is substantially the same as that of the conventional construction in which the spring is attached to a neck on the brush, which does not prevent chatter. Thus, the new construction makes it possible to eliminate brush chatter without the increased cost which has previously been involved. This new result is obtained in a simple manner by using a brush with inclined top surface and loosely attaching the spring to the brush by means of the hole i i and hook l2, so that the spring and brush can readily be removed or inserted as a unit, and the spring itself can be used to conduct current to or from the brush since it is held in direct contact with the brush. Thus a simple, low cost construction is provided which makes it possible to eliminate brush chatter without any increase in cost. This is an important advantage in brush mechanisms for use in small universal motors where any increase in cost is a very serious matter.

A specific embodiment of the invention has been shown and described for the purpose of illustration, but it will be obvious that various modifications may be made within the scope of the invention. It is to be understood therefore that the invention is not limited to the specific details shown, but in its broadest aspects, it includes all equivalent embodiments and modifications which come within the scope of the appended claims.

I claim as my invention:

1. In combination, a tabular brushholder having a rectangular axial slot therein, a brush disposed in said slot, said brush having its upper surface inclined with respect to the axis of the brushholder and of the brush, a cap closing the top of the brushholder, and a compression spring in the slot directly engaging the inclined upper surface of the brush, said spring being attached to the brush, the pressure of the spring on the inclined upper surface of the brush holding the brush against one side of the brushholder throughout the length of the brush.

2. In combination, a tubular brushholder having a rectangular axial slot therein, a brush disposed in said slot, said brush having its upper surface inclined with respect to the axis of the brushholder and of the brush, a cap closing the top of the brushholder, and a compression spring in the slot directly engaging the inclined upper surface of the brush, the brush having a transverse hole therethrough near its upper end, and the spring having a hook portion at its lower end passing through said hole to attach the spring tothe brush, the pressure of the spring on the inclined upper surface of the brush holding the brush against one side of the brushholder throughout the length of the bush.

3. In combination, a tubular brushholder having a rectangular axial slot therein, a brush disposed in said slot, said brush having its upper surface inclined with respect to the axis of the brushholder and of the brush, a cap closing the top of the brushholder, and a helical compression spring of conducting material in the slot, said spring having its upper end clamped between said cap and the upper end of the brushholder, and the lower end of the spring directly engaging in the inclined upper surface of the brush and being loosely attached to the brush, the pressure of the spring on the inclined upper surface of the brush holding the brush against one side of the brushholder throughout the length of the brush.

4. In combination, a tubular brushholder having a rectangular axial slot therein, a brush disposed in said slot, said brush having its upper surface inclined with respect to the axis of the brushholder and of the brush, a cap closing the top of the brushholder, and a helical compression spring of conducting material in the slot, said spring having its upper end clamped between said cap and the upper end of the brushholder, the lower end of the spring directly engaging the inclined upper surface of the brush, the brush having a transverse hole therethrough near its upper end. and the spring having a hook portion at its lower end passing through said hole to attach the spring to the brush, the pressure of the spring on the inclined upper surface of the brush holding the brush against one side of the brushholder throughout the length of the brush.

WILLIAM H. MITCHELL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,206,366 Redmond July2, 1940 2,264,998 Miner ii Dec. 2, 1941 2,391,005 Bryan Dec. '18, 1945 FOREIGN PATENTS Number Country Date 565,821 Germany Dec. 8, 1932 

